Riga only took charge at Bloomfield Road in June, but has struggled to put a competitive squad together to compete in the second tier.
Having had a squad of just eight players - with no goalkeeper - a month before the campaign got under way, a scatter-gun approach to recruitment has not served them well with just one victory to their name.
The Lancashire club's troubles led to a frosty relationship between the manager and chairman Karl Oyston, who claimed Riga had acted unprofessionally by returning to Belgium without permission during September's international break.
Saturday's 3-0 defeat to Reading was their 10th from 14 games this term and was the last straw for Oyston and the club confirmed on Monday that Riga had been removed from his role.
"Blackpool Football Club can confirm that head coach Jose Riga has had his contract terminated with immediate effect," the club announced on their official website.
No details of Riga's replacement have been revealed by the club, leaving it uncertain who will be in charge when they welcome Ipswich Town on Saturday.
